As a fellow person who uses unreal. i'm not really sure what to say since its not my cup of tea game. some feedback ill give is:
gameplay: too simple and not intuitive imo, its not fun and its just moving and do space bar,
graphics: except for the character model and some models, you are lacking vfx.
innovation: you are toggling the visibility in the char only possibly the char hidden in game, when you are "swimming" you need to add something to notify where u are at least like floating backpack or some water vfx, animations are built-in, like i said before gameplay is moving and doing space bar
theme: its minimum imo but passable
polish: it looks severely unpolish for me